NEW YORK — Barely 20 minutes after another lopsided loss to the St. Louis Cardinals, this time by a score of 9-2, the New York Mets’ clubhouse was quiet and unusually empty. And David Peterson, whose nightmare season continued with another rough outing, had already left the premises.After starter Austin Warren’s lone inning, Peterson allowed six runs in 3 2/3 innings, including home runs to Nelson Velázquez and Jordan Walker.Whatever positive momentum Peterson had built in the first half of May has dissipated again. After a four-game stretch with three wins and a 2.50 ERA, he’s allowed 12 runs in his last 12 2/3 innings. Wednesday’s performance pushed the 2025 All-Star’s ERA back up to 5.75.“He left a couple pitches there, and they hit him hard,” manager Carlos Mendoza said.It’s the fourth time in 14 appearances that Peterson has allowed at least six runs. He had never done that more than three times in a major-league season. He had allowed six or more runs in three of his 51 starts spanning 2024 and 2025.Peterson has been inconsistent with his command all season. He’s missed up with his sinker and to his arm side with his four-seamer. In the biggest confrontation of Wednesday night, he left a four-seamer in the middle of the plate to St. Louis’ most dangerous hitter. Walker smashed it for a three-run homer to push the lead to 7-0.The guy who carried the Mets’ staff for months at a time last season, when he was the only starter capable of pitching through six innings, hasn’t lasted more than 5 1/3 in an outing this season.And Peterson, who as the longest-tenured Met has grown into a leadership role in the clubhouse, departed before the typical postgame session with reporters — suggesting just how frustrating this season has become for him. After other poor outings this season, Peterson adamantly expressed his confidence that he would turn it around.“He’s a strong-minded person,” said Francisco Alvarez, whose two-run homer Wednesday is all the offense the Mets have mustered in 18 innings this week. “He always finds a way to get out of it.”“He’s a good pitcher, and we’ve seen flashes,” Mendoza said. “He’s a guy we’re going to need to get big outs for us.”The Mets are running out of ideas with Peterson. They’ve tried him as a conventional starter and behind an opener. They’ve paired him more consistently with Luis Torrens rather than Alvarez. The changes haven’t led to the kind of long-term turnaround they’ve hoped for.“Keep going with him,” Mendoza said of the plan moving forward. “We need him. We’ve got to help him.”It was the 10th time this season, and fourth time in eight games this month, that the Mets have used an opener in front of a starter-turned-bulk-reliever. They’re 4-6 in those contests, though they’ve actually allowed fewer runs per game with an opener than without.Wednesday was the worst it’s looked, with Warren giving up two runs in the first before Peterson took over. But the problem has been less the strategy and more the need for it. It’s a concession to the backward steps taken by Peterson and Sean Manaea, neither of whom the Mets trust to face the top of an opposing order a third time anymore.Peterson’s slide is emblematic of the Mets’ woes with the depth of their starting pitching. They entered the season boasting seven established major-league starters, all of whom made it through spring training healthy for once, plus two more starters with major-league experience in Triple A.But very little has gone according to plan for a chunk of that group. Manaea has yet to start a big-league game this season, relegated to the bullpen by lagging velocity in the spring. He has taken encouraging steps of late, emerging as a viable bulk option (as opposed to the mop-up man he was earlier in the season) with his velo rebounding. Still, Manaea has thrown more than four innings just one time this season.Kodai Senga struggled before landing on the injured list with inflammation in his back. His rehab assignment has been uneven, with suboptimal results, mechanical tinkering and a minor setback earlier this week.The trio of Peterson, Manaea and Senga has combined for a 6.02 ERA this season over 123 innings. New York doesn’t need all of them to click as top-of-the-rotation guys. But the Mets can’t afford for all three to flop like this.